Nickel plating



NICKEL PLATING Donald Gardner Foulke, Watchung, and Otto Kardos,

Red Bank, N. J., assignors to Hanson-Van Winkle- Munning Company, a corporation of New Jersey No Drawing. Application December 28, 1956 Serial No. 631,028

Claims. (Cl. 204 -49) This invention relates to nickel plating and, more par- 2,818,376 Patented Dec. 31, 1957 2 effective to reduce skip plating, and to extend the bright plating capacity of the bath (when it contains a primary brightening addition agent) to very low current densities.

There appears to be no critical upper limit as to the con-- 7 Thiomalic acid may be used with particular advantage.

. in a nickel plating bath which also contains a strong ticularly, to electrodepositing nickel (bright nickel in particular) from an aqueous acidic -nickel electroplating bath. The invention provides an improved process, based on the use of an improved nickel plating bath containing thiomalic(mercapto-succinic) acid for producing nickel electrodeposits which are substantially free from cloud, haze, and skip defects and which can be formed bright or brilliant over a wide current density range.

The operating requirements imposed upon commercial high-speed nickel electroplating processes are governed by several factors other than obtaining maximum brightness. A commercially bright nickel process should produce electroplates of high brilliance over a wide current density range extending from over 100 to as little as 1 or 2 amperes per square foot. It should exert a pronounced leveling efliect, and the electroplate formed should be resistant to corrosion and have a high ductility and a low stress. In commercial operations when it is desired to complete the plating operation as rapidly as possible, the highest practical average current density should be'employed; and since high current densities generally involve high bath temperatures, the installation should be amenable to operation at temperatures from 50 C. to 80 C. Under these commercially desirable conditions even the best of the heretofore known bright nickel plating baths sometimes tend to form hazy or cloudy deposits, especially at the very low current density areas of the object being plated.

Sometimes it is necessary or advisable to operate at low pH values, near or below 3.0, a condition which promotes incomplete covering of the basis metal and so results in unplated spots (especially common on copper and brass). plating, is accentuated by the presence of traces of metallic impurities, such as lead and zinc, in the plating bath. Addition agents which are effective for promoting bright and level deposits, and for extending the current density range over which such deposits are formed, are not generally effective for preventing skip plating. Indeed, sometimes they may even favor it.

We have found that the incorporation in acidic aqueous nickel electroplating baths of a fraction of a gram per liter of thiomalic acid reduces the tendency for skip plating to occur, even under conditions which strongly favor the skip defect. It also is effective for reducing the tendency for cloudy areas to form in regions of very low current density. Thus its presence in the bath facilitates operation of the electroplating process at high temperatures and at low pH, and with high tolerance for impurities such as lead and Zinc. Further, the presence of thiomalic acid in the bath has the effect of extending to very low current density valuesthe current density range over which bright deposits can beforrned when a brightening addition agent is also present:

In general, the addition of thiomalic acid to the plating Thisphenomenon, which is known as skip (class II) brightener. We have obtained particularly satisfactory results using it together with water-soluble acetylenic compounds such as oxygen-containing and aminosubstituted acetylenic compounds, alone or in combination with various sulfo-oxygen compounds. Examples of oxygen-containing acetylenic compounds which we have used successfully in embodiments of this invention are set forth (as group A Compounds) in the Kardos, Menzel and Sweet U. S. Patent No. 2,712,522. These 7 acetylenic compounds can be represented by the following i in which R, and R are selected from the group consisting bath in concentrations as low as 0.005 gram per liter is of hydrogen and alkyl and hydroxy-substituted alkyl radicals containing one to four carbon atoms, R is selected from the group consisting of hydroxy, hydroxymethyl, methoxy, hydroxyethyl, ethoxy, and hydroxyethoxy radicals, and R is selected from the group consisting of hydrogen, halogen, diethylaminoethyl, morpholinomethyl, alkyl, alkenyl, alkynyl and hydroxy-, methoxy-, and ethoxy-substituted alkyl, alkenyl, and alkynyl radicals containing from one to four carbon atoms., These watersoluble acetylenic compounds may be used over a wide range of concentrations, but preferably are used in an amount in the range from about 0.05 to about 3 grams per liter. Examples of acetylenic amine compounds that have been used successfully in conjunction with thiomalic acid in the process of this invention may be selected from the group consisting of monoacetylenic primary monoamines, monoacetylenic polyamines, polyacetylenic monoamines, polyacetylenic polyamines, acetylenic alkanolamines, and acetylenic ammonium compounds. These acetylenic amine componnds are preferably used in concentrations from 0.005 to 1 gram per liter.

Thiomalic acid also may be used with advantage in plating baths containing a sulfo-oxygen compound, either alone or in combination with a strong brightener of the acetylenic type. The compounds listed as Group B Compounds in the aforesaid Kardos, Menzel and Sweet U. S. Patent No. 2,712,522 are examples of representative sulEo-oxygen compounds which have been used successfully in combination with a water-soluble acetylenic compound to promote the formation of brilliant and ductile nickel deposits. They include unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, heterocyclic sulfonic acids, mononuclear sulfinic acids, alkali metal, ammonium, magnesium and nickel salts of such acids, and mononuclear aromatic sulfonamides and sulfonimides. These sulfo-oxygen compounds may be used over a very wide range of concentrations t to grams per liter), but preferably are used in an amount in the range from about 1 to about.

40 grams per liter.

It is of course understood that the use of thiomalic acid in accordance with this invention is not limited to baths in which one or more of the above-described acetylenic or sulfa-oxygen compounds is incorporated. On

the-contrary, thiomalic acid can be used with advantage in baths containing other brightening agents; and it can be used with advantage to reduce skip plating and other deleterious effects of such impurities as zinc in nickel plating baths containing no brightening agent at all.

The following examples are illustrativeof the effectiveness with which thiomalic acid may be used in accordance with this invention:

Example I A highly purified Watts nickel plating bath was prepared containing 412.5 grams per liter of nickel sulfate, 75 grams per liter of nickel chloride, 41.3 grams per liter of boric acid, 15 grams per liter of sodium naphthalene- 1,3,6-trisulfonate, 0.2 gram per liter of 2-butyne-l,4-diol,

and 0.02 gram per liter of an anti-pitting agent (sodium lauryl sulfate). After adjusting the pH of the bath to 2.5 with sulfuric acid, an electrodeposit of nickel was formed on a bent panel of polished brass, using a bath temperature of 60 C.', vigorous air agitation; andan' scribed increased the haziness of the deposit formed-n a test, panel. This defect wascompletely eliminated, after, 0.03 gram per liter of thiomalic acid wasaddedto thezinc-contaminated plating bath, and theelectroplate formed on bent test panels was fully brilliant and ductile at ,all average current densities in therange from 15 to 90 amperes per square foot.

Example Il Although theincidence of haze, streaks,;and skips can' be appreciablyreduced by operating the bath at arelatively high pH, low temperature, and low concentration of nickel, the presence of even a very small concentration of zinc in the plating bath (such as can easily-accumulate.

due to chemical attack by the bath,on brassiarticles being plated) tends to disrupt the favorable operating conditions.

and results in black streaked deposi t s.

U'sing a bath temperature of 50 C. at; a;pI -I of 3.5 and without agitation, a brilliant nickel electrodeposit was formed over almost the entire current density range in a Hull test cell from a purified Watts nickel plating.

bath containing 300 grams per (liter ofnickel; sulfate, 45 grams per liter of nickel chloride, 41.25 grams per liter of boric acid, 15 grains per liter of sodium naphthalene- 1,3,6-trisulfo'nate, 0.3 gram per liter of 2-butyne -1,4-. diol, and, 009 gram per liter.of an anti-pitting agent (sodium lauryl sulfate).

most of the test panel. liter of thiomalic acid. to the zinc-bearing plating bath,

the deleterious effects of. the zinc contamination were completely counteracted and .a. brilliant nickel deposit formed over theentire current density range of the panel.

Example III A brilliant nickel deposit wasformed on a polished brass panel 'in aHullcell, using a plating bath and plating conditions similar tothos'e, described in Example I,

with the sole exception that 0.2 gram per liter of N-diethyh propargyl. amine hydrochloride -was used in; the bath, in,

p se 7 .5; 2:b tyt -d' 91-L e-addi i n. of; Liz-51.8 7 su fate qth s bath. rendered ,theelectLoa i l baa-e 4 aw nes np per liter of j'zi p atel .aji est P,

Upon adding 0.01 gram When 1.8 grams per liter of; zinc sulfate were added to this plating bath, the electroplate formed from it became streaked and black over. By addingonly 0.03 gram-per,

areas. Upon the subsequent addition of 0.03 gram per liter of thiomalic acid to the bath, these defects were eliminated and a continuous fully brilliant electrodeposit was obtained over the entire current density range.

' Example IV Thiomalic acid has also proved exceptionally effective in nickel plating baths containing rosaniline-type brightening additives. A brilliant electroplate was formed on a test panel in a Hull cell by using a plating bath and plating conditions similar to that described in Example I, but with the exception that 0.1 gram per liter of bis-paminophenyl-4-amino m-tolylcarbinol (fuchsin) was employed in place of 2-butyne-1,4-diol. When 1.8 grams per liter of zinc sulfate were added to the plating bath, a black streaked deposit formed over almost the entire length of the test panel. This harmful effect of zinc contamination was eliminated and the conditions necessary to formation of a brilliant nickel electrodeposit were reestablished upon the addition to the plating bath of substantially 0.04 gram per liter of thiomalic acid.

Example V When nickel was electrodeposited in a Hull test cell at 50 'C. from a high-chloride plating'bath -(pH=3.5)

containing grams per liter of nickelsulfate, 248 grams per liter of nickel chloride, 41.2 grams per liter of boric acid, 30 grams per liter of sodium naphthalene-1,3,6- trisulfonate, 2 grams per liter of o-sulfobenzoic imide,

and 0.3 gramper liter of 2-butyne-1,4-diol, the resultant electroplate was marred by a strong haze in the medium current density range of the test panel. Upon the addition of 0.015 gram per liter of thiomalic acid to the bath,

a brilliant nickel deposit was formed over the entire currentdensity range of the test panel.

Example, VI

When a bright plating bath is contaminated by lead A nickel plating bath containing'320 grams per liter' of nickel sulfate, 45 grams per liter of nickel chloride,

41.3 grams per liter of boric acid, 15 grams per liter of sodium naphthalene-1,3,6-trisulfonate, 0.3 gram per liter of 2-butyne-1,4-diol, and 0.09 gram per liter of an antipitting agent (sodium lauryl sulfate) was saturated withlead chloride and filtered prior'to use. After adjusting the pH to 3.5 with sulfuric acid,-the bath was employed in a Hull cell at 50 C. and yielded a bright electroplate, but one which only poorly covered the low current density area of the test panel. Upon the addition of 0.02 gramper liter;of thiomalic acid tov the;bath, a bright deposit free from skipped areas was formed over the entire current density range.

Example VII Thiomalic acid along with a brightener of the acetylenic type makes it possible to obtain bright nickel electrode: posits in the absence of the sulfo-oxygen compounds under conditions which call for the presence of the latter. In,

a Watts bath of the basic inorganic salt composition of Example II, containing 0.2 gram per liter of 2-butyne1,4- diol, semi-bright deposits were obtained at 40 amperes per square foot, a pH of 3.5, and a bath temperature of 55 C. with air agitation. However, when 0.04 gram per liter of thiomalic acid was added, the nickel deposit formed under these same conditions was fully bright Although the basis or reaction mechanism by whi ch thiomalic'acid functions is not understood, it is evident from the foregoing examples that incorporating thiomalic acid in an acid nickel plating bath'allows the plating oper ation ;to, ;,be.c.carried; outat high temperatures and a low This defect pH without danger of obtaining hazy, streaked or skipped deposits at the cathode.

Example VIII While thiomalic acid is particularly beneficial in nickel plating baths containing strong brighteners, it can be used with advantage in plating from baths containing no other addition agent. A plain Watts bath having substantially the composition (in nickel sulfate, nickel chloride, and boric acid) of Example I was contaminated with 1.8 grams per liter of zinc sulfate (such as might accumulate in the solution over a period of time during which brass or zinc alloy die castings were being plated). The deposit formed on a test panel at 50 C. and at a pH of 3.5 was black and easily peeled from the panel in the areas of middle and high current densities. Upon adding 0.24 gram per liter of thiomalic acid, a normal grayish deposit which did not tend to peel was formed under the same temperature and pH conditions over substantially the entire current density range of the test panel, and this deposit even tended to be bright in the high current density areas.

The foregoing examples show the advantages attained when thiomalic acid is used in a Watts nickel plating bath, which is prepared by dissolving nickel sulfate and nickel chloride in water and containing also boric acid. Similar advantages also are attained when thiomalic acid is dissolved in other types of aqueous acidic nickel electroplating baths. For example, its use is beneficial in straight nickel sulfate baths, in straight nickel chloride baths, and in such other aqueous nickel electroplating baths as those based on using nickel formate, nickel sulfamate, or nickel fiuoborate as the nickel salt which is dissolved in the aqueous acidic solvent. The invention therefore contemplates the use of thiomalic acid in any aqueous acidic nickel electroplating bath.

We claim:

1. A process for nickel plating which comprises electrodepositing nickel on a basis metal from an aqueous acidic solution of at least one nickel salt in which there is dissolved from about 0.005 to about 0.5 gram per liter of thiomalic acid.

2. A process for nickel plating which comprises electrodepositing nickel from an aqueous acidic solution of at least one nickel salt in which there is dissolved from 0.01 to 0.2 gram per liter of thiomalic acid.

3. A process for producing a bright nickel electrodeposit which comprises electrodepositing nickel on a basis metal from an aqueous acidic solution of at least one nickel salt in which there is dissolved a brightening addition agent and from about 0.005 to about 0.5 gram per liter of thiomalic acid.

4. The process for producing a bright nickel electrodeposit which comprises electrodepositing nickel on a basis metal from an aqueous acidic solution of at least one nickel salt in which there is dissolved from 0.05 to 3 grams per liter of a water-soluble acetylenic compound and from about 0.01 to about 0.2 gram per liter of thiomalic acid.

5. The process for producing a bright nickel electrodeposit which comprises electrodepositing nickel on a basis metal from an aqueous acidic solution of at least one nickel salt in which there is dissolved from about 0.05 to about 3 grams per liter of a water-soluble acetylenic compound, from about A to about grams per liter of a water-soluble sulfo-oXygen compound, and from about 0.01 to about 0.2 gram per liter of thiomalic acid.

6. An aqueous acidic nickel electroplating bath comprising an aqueous solution of at least one nickel salt in which there is dissolved from about 0.005 to about 0.5 gram per liter of thiomalic acid.

7. A nickel electroplating bath comprising an aqueous acidic solution of nickel sulfate and nickel chloride in which there is dissolved from 0.01 to 0.2 gram per liter of thiomalic acid.

8. A plating bath for producing bright nickel electrodeposits comprising an aqueous acidic solution of at least one nickel salt in which there is dissolved a brightening addition agent and from 0.005 to 0.5 gram per liter of thiomalic acid.

9. A plating bath for producing bright nickel electrodeposits comprising an aqueous acidic solution of at least one nickel salt in which there is dissolved from 0.05 to 3 grams per liter of a water-soluble acetylenic compound and from about 0.005 to about 0.5 gram per liter of thiomalic acid.

10. A plating bath for producing bright nickel electrodeposits comprising an aqueous acidic solution of nickel sulfate and nickel chloride in which there is dissolved from about 0.05 to about 3 grams per liter of a watersoluble acetylenic compound, from about A to about 80 grams per liter of a water-soluble sulfo-oxygen compound, and from about 0.005 to about 0.2 gram per liter of thiomalic acid.

References Cited in the file of this patent UNITED STATES PATENTS 570,554 Jordis Nov. 3, 1896 2,523,161 Struyk et al Sept. 19, 1950 2,712,522 Kardos et a1. July 5, 1955 

1. A PROCESS FOR NICKEL PLATING WHICH COMPRISES ELECTRODEPOSITING NICKEL ON A BASIS METAL FROM AN AQUEOUS ACIDIC SOLUTION OF AT LEAST ONE NICKEL SALT IN WHICH THERE IS DISSOLVED FROM ABOUT 0.005 TO ABOUT 0.5 GRAM PER LITER OF THIOMALIC ACID. 